Early electrodiagnosis of the ulnar entrapment neuropathy at the elbow.

Reliable, technically not demanding, electrophysiological tests make it possible to diagnose the ulnar entrapment neuropathy at the elbow. Ulnar nerve was stimulated supramaximally at the wrist, below and above the elbow, and in the upper arm, and the sensory nerve action potential (SNAP) and compound muscle action potential (CMAP) were recorded. Sensory and motor nerve conduction velocities (SNCVs, MNCVs) were calculated in each segment. In 12 of 64 symptomatic extremities of 44 patients with a presumptive diagnosis of the ulnar neuropathy at the elbow MNCVs of all segments were within normal limit and only SNCV across the elbow was significantly slowed (p less than 0.001). In 25 extremities of the patients SNAP was not obtained. Evidence of denervation in the first dorsal interosseous and abductor digiti minimi muscles was detected in about 50% hands tested. This percentage was higher in the hands with absence of SNAP than those with presence of SNAPs. It would appear that measurement of SNCV across the elbow is a more sensitive parameter to detect abnormal conduction across the cubital tunnel in patients with the ulnar neuropathy.